FIRE SAFETY AND BROOF(T4): UPDATES EXPLAINED

In July 2017, following the Grenfell fire, the Chair of the Independent Review of Building Regulations and Fire Safety, Judith Hackitt, issued a report reviewing the Building Regulations 2010. The conclusion: a more robust regulatory system for the construction industry is called for. The British government responded to the Hackitt report by issuing the Building (Amendment) Regulations 2018 – banning the use of combustible materials in the external walls of buildings – and by adapting the Approved Documents that accompany the Building Regulations 2010. These Documents provide practical guidance on how building professionals can achieve compliance. Among them was the Approved Document B (ADB) on fire safety.

The 2019 edition of ADB brought along several changes affecting roofing. For one, the principal determinant of external fire performance for roofs is no longer the national classification system BS 476-3:2004, but the European classification system BS EN 13501-5 (which ran alongside the national classification system for years). The latter comes with five European class ratings: B_ROOF(t4), C_ROOF(t4), D_ROOF(t4), E_ROOF(t4) and F_ROOF(t4). In what follows, we explain the details of the fire standards for roofs and how they correspond to the old classification system. We will also provide an overview of SOPREMA waterproofing systems that have a B_ROOF(t4) rating, indicating the highest performance.

If you want to know more about Requirement B4 and the recent understanding on the term ‘specified attachment’ that has been reached in line with the new BS8579 ‘Guide to the Design of Balconies and Terraces’, we’d like to refer you to our article on the updated ban on combustible materials.

REGULATION 7(2)

Among other requirements, the Building Regulations 2010 stipulate that

√“The external walls of the building shall adequately resist the spread of fire over the walls and from one building to another, having regard to the height, use and position of the building.”

√“The roof of the building shall adequately resist the spread of fire over the roof and from one building to another, having regard to the use and position of the building.”

To meet those demands, regulation 7(2) prescribes that “materials which become part of an external wall, or specified attachment, of a relevant building are constructed of materials rated A2-s1,d0 or A1 in line with Classification BS EN 13501-1”.

BS EN 13501-5 AND ITS 4 ROOF TESTS

BS EN 13501-5 classification refers to four separate roof testing methods (DD CEN/TS 1187:2012) that measure the performance of roofs. Test 1 with burning brands, test 2 with burning brands and wind, test 3 with burning brands, wind and supplementary radiant heat.

Test 4 evaluates the performance of a roof under the conditions of thermal attack with burning brands, wind and radiant heat. The test gauges external fire spread and penetration by fire. One specimen is examined in the preliminary test. Three other specimens are assessed in the penetration test, with at least one specimen containing samples of the joint details in each layer of the roof system. The suffix (t4) indicates that Test 4 is to be used, with B_ROOF(t4) indicating the highest performance and F_ROOF(t4) the lowest.

B_ROOF(T4) TO F_ROOF(T4)

Based on test 4, we arrive at the following classification system for roofs and roof coverings exposed to external fire:

BS EN 13501-5 classification (newer) Classification using data from external fire exposure to roof tests [2016] (European standards)	BS 476-3 classification (former) BS 476-3 classification and testing method for external fire exposure to roofs [2004]
B_ROOF(t4)	AA, AB or AC
C_ROOF(t4)	BA, BB or BC
D_ROOF(t4)	CA, CB or CC
E_ROOF (t4)	AD, BD or CD
F_ROOF (t4)	DA, DB, DC or DD

√B_ROOF(t4)

No penetration of roof system within 60 minutes

In preliminary test, after withdrawal of the test flame, specimens burn for less than 5 minutes

In preliminary test, flame spread less than 0.38 m across region of burning

√C_ROOF(t4)

No penetration of roof system within 30 minutes

In preliminary test, after withdrawal of the test flame, specimens burn for less than 5 minutes

In preliminary test, flame spread less than 0.38 m across region of burning

√D_ROOF(t4)

Roof system is penetrated within 30 minutes but is not penetrated in the preliminary test

In preliminary test, after withdrawal of the test flame, specimens burn for less than 5 minutes

In preliminary test, flame spread less than 0.38 m across region of burning

√E_ROOF (t4)

Roof system is penetrated within 30 minutes but is not penetrated in the preliminary test

Flame spread is not controlled

√F_ROOF (t4)

No performance determined

CORRESPONDENCE TO BS 476-3:2004

For purposes of clarification, the roof covering classification BS EN 13501-5 is transposed to the former national classification system in the table below:

LIMITATIONS ON ROOF COVERINGS

With the classifications ranging from B_ROOF(t4) to F_ROOF (t4) also come certain separation distances or minimum distances from the roof, or part of the roof, to the so-called ‘relevant boundary’. Approved Document B defines a relevant boundary as: “the boundary or notional boundary (a boundary presumed to exist between two buildings on the same site) that one side of the building faces and/or coincides with, and that is parallel or at an angle of a maximum of 80 degrees to that side of the building.”

B_ROOF(t4)	Unrestricted; can be used anywhere on the roof
C_ROOF(t4)	At least 6 m from the boundary
D_ROOF(t4)	At least 6, 12 or 20 m from the boundary (depending on the building type and use)
E_ROOF (t4)	At least 6, 12 or 20 m from the boundary (depending on the building type and use)
F_ROOF (t4)	At least 20 m from the boundary

JUNCTION OF COMPARTMENT WALL WITH ROOF

Approved Document B also includes regulations on compartmentation, which reduces the spread of fire (with fire stopping in walls and floors) in paragraphs 5.12 to 5.14:

√“To reduce the risk of fire spreading over the roof from one compartment to another, a 1500 mm wide zone of the roof, either side of the wall, should have a covering classified as BROOF(t4), on a substrate or deck of a material rated class A2-s3, d2 or better.”

√“Materials achieving class B-s3, d2 or worse used as a substrate to the roof covering and any timber tiling battens, fully bedded in mortar or other suitable material for the width of the wall, may extend over the compartment wall in buildings that are a maximum of 15 m high.”

√“Double-skinned insulated roof sheeting should incorporate a band of material rated class A2-s3, d2 or better, a minimum of 300 mm in width, centred over the wall.”

A visualisation will make this more clear:

Approved Document B includes an alternative to the provisions of paragraphs 5.12 to 5.14, too: in two cases, “the compartment wall may extend through the roof for a minimum of either of the following (see Diagram 5.2c)”, namely: “where the height difference between the two roofs is less than 375 mm, 375 mm above the top surface of the adjoining roof covering” and “200 mm above the top surface of the adjoining roof covering where either of the following applies: a) the height difference between the two roofs is 375 mm or more, or b) the roof coverings either side of the wall are of a material classified as BROOF(t4).”